Abstract: The invention provides novel isomers of dihydrotetrabenazine, individual enantiomers and mixtures thereof wherein the dihydrotetrabenazine is a 3,11 b-cis-dihydrotetrabenazine. Also provided are methods for the preparation of the novel isomers, pharmaceutical compositions containing them and their use in treating hyperkinetic movement disorders such as Huntington's disease, hemiballismus, senile chorea, tic, tardive dyskinesia and Tourette's syndrome.